Here's my 2 cents (maybe less depending on if you agree with me)... ;-)
Hackers -- I'd rather see the "malicious advice" posted here in the open for ALL sysadmins to see than one some deep dark secret haxor board that only a handful of troublemakers know about.
Cheaters -- My mommy told me cheaters never win. Boy was she wrong. ;-) That being said, I can't say I personally care TOO much about someone trying to crowd-source their homework. They can't crowd-source their exams... so... if the crowd gave them answers to help them better understand the subject, so be it. If they didn't understand, then look on the bright side... at least their learned the basic steps of OUTSOURCING... let's make those people MANAGERS. wicked grin
Lusers -- This kinda goes back to the whole "Hackers" thing. I too have seen questions about getting around proxy servers, etc. On the same note, I've also seen questions from sysadmins who have REALIZED the system is being circumvented and are asking for ways to lock it down harder/better. I think its a win-win personally. I'm not a big fan of "pretending" a vulnerability doesn't exist.
How do you decide to answer suspicious questions? -- I answer the ones I feel are worth answering... which is most of them that I feel I can contribute a good answer to. REMEMBER, the answer isn't just for the poster... its for the community as a whole and for future sysadmins that may stumble upon the question weeks or even months from now.
What ethical responsibilities do we have as a community? -- Well I wouldn't post something that is completely damaging, such as a zero day exploit. Other than that, knowledge is knowledge. Most of the answers here can be found elsewhere on the internet... its just easier and more convenient to have them all in one place. That place is ServerFault, StackOverflow, etc.
Are there questions that shouldn't be answered? -- Within reason, no. I personally wouldn't respond to a question like, "I'm trying to hack www.example.com, can someone out there give me tips?" or "How do I attack www.example.com?" or something clearly malicious.